The present invention relates to an electric steering apparatus using a motor as a source of generating a steering assist force.
An automobile is steered by transmitting a rotational operation of a steering wheel disposed inside the compartment of the vehicle to a steering mechanism provided outside of the compartment for steering-control wheels (in general, front wheels).
FIG. 1 is a cross-sectional view of an electric steering apparatus according to a conventional example.
As illustrated in FIG. 1, an electric steering apparatus for an automobile comprises a first steering shaft 101 connected to a steering wheel; a torque sensor 104 for detecting a steering torque by relative displacement in a rotating direction between the steering shaft 101 and a second steering shaft 103 connected to the steering shaft 101 through a torsion bar 102; and a reduction mechanism 108 including a hypoid pinion 106 for increasing a torque of a steering assisting motor 105 driven based on a torque detected by the torque sensor 104 and for transmitting the increased torque to the steering shaft 103 and a hypoid wheel 107 meshing with the hypoid pinion 106, and is arranged to assist the operation of the steering mechanism corresponding to the rotation of the steering wheel by rotation of the motor 105 so as to reduce a driver""s labor for steering.
The hypoid pinion 106 is integrally coupled to one end portion of a rotating shaft 109 of the motor 105. Moreover, movement of the hypoid pinion 106 in a radial direction and in an axial direction is inhibited by a pair of bearings 110 and 111 supporting both end portions of the rotating shaft 109, while a pair of bearings 112 and 113 prevent the second steering shaft 103 to which the hypoid wheel 107 is attached from moving in a radial direction and in an axial direction.
By the way, in the case where the hypoid pinion 106 and hypoid wheel 107 are used, the clearance between the teeth of the hypoid pinion 106 and hypoid wheel 107 is initially set in assembling. At this initial setting, a variation of the clearance between the teeth is caused by dimensional errors of parts, such as the hypoid pinion 106, bearings 110 through 113, hypoid wheel 107 and second steering shaft 103, and the accuracy of the crossing angle in assembling. Consequently, backlash occurs after the assembling, and noise caused by this backlash will be heard inside the compartment of the automobile.
Further, with the progress in an increase of the power of the steering assist force in resent years, the abrasion of the teeth of the hypoid pinion 106 and hypoid wheel 107 increases and a problem arises that occurrence of the above-mentioned backlash is unavoidable. In this case, since the movements of the hypoid pinion 106 and hypoid wheel 107 are inhibited, the backlash can not be adjusted and consequently noise caused by the backlash will be heard inside the compartment of the automobile.
An object of the present invention is to provide an electric steering apparatus capable of solving the above problems.
An electric steering apparatus according to the first invention is an electric steering apparatus for assisting steering by rotation of a motor, comprising: a driving gear provided on a supporting shaft which operates with rotation of the motor for assisting steering; a driven gear meshing with the driving gear; a steering shaft to which the driven gear is provided; and a first bearing for supporting the supporting shaft; and characterized in that the driving gear can deflect in the radial direction, and deflecting means for deflecting the driving gear in its deflecting direction is comprised.
An electric steering apparatus according to the second invention is characterized, in addition to the first invention, in that the deflecting means includes an elastic member having at least three protrusions for energizing the driving gear in the deflecting direction from at least three positions along a circumferential direction.
An electric steering apparatus according to the third invention is characterized, in addition to the first invention, in that the driving gear is able to swing with the first bearing as a fulcrum.
An electric steering apparatus according to the fourth invention is characterized, in addition to the third invention, in that the deflecting means includes an elastic member having at least three protrusions for energizing the driving gear in the deflecting direction from at least three positions along a circumferential direction.
An electric steering apparatus according to the fifth invention is characterized, in addition to the third invention, in that the supporting shaft is a rotating shaft of the motor, and one end portion of the supporting shaft is supported so that it is able to swing with the first bearing as a fulcrum, the other end portion of the supporting shaft of the motor is supported by a second bearing which is deflectable in a radial direction, and the driving gear is integrally coupled to the one end portion of the rotating shaft.
An electric steering apparatus according to the sixth invention is characterized, in addition to the fifth invention, in that the deflecting means is interposed between the second bearing and a housing for holding the second bearing.
An electric steering apparatus according to the seventh invention is characterized, in addition to the fifth invention, in that the deflecting means includes an elastic member having at least three protrusions for energizing the driving gear in the deflecting direction from at least three positions along a circumferential direction.
An electric steering apparatus according to the eighth invention is characterized, in addition to the third invention, in that both end portions of the rotating shaft of the motor are supported by a pair of third bearings, and the driving gear is coupled to one end portion of the rotating shaft through a universal joint.
An electric steering apparatus according to the ninth invention is characterized, in addition eighth invention, in that the deflecting means includes an elastic member having at least three protrusions for energizing the driving gear in the deflecting direction from at least three positions along a circumferential direction.
An electric steering apparatus according to the tenth invention is characterized, in addition to the eighth invention, in that the driving gear is supported by a fourth bearing interposed between the first bearing and the universal joint so that it is deflectable in a radial direction, and the deflecting means is an elastic member for energizing the fourth bearing in its deflecting direction.
An electric steering apparatus according to the eleventh invention is characterized, in addition to the first invention, by further comprising fifth and sixth bearings made of iron for limiting movement of the driven gear in an axial direction; and an elastic member, interposed between the fifth bearing and a housing made of aluminum into which the fifth and sixth bearings are fitted, for energizing the fifth bearing toward the driven gear, and in that the driven gear is formed by using a hypoid wheel.
According to the first invention, since the driving gear can be deflected toward the driven gear by the deflecting means, it is possible to satisfactorily eliminate backlash without being affected by dimensional errors of parts such as the driving gear and the accuracy of the crossing angle in assembling and to improve the yield. Moreover, even when the meshing state of the driving gear and driven gear changes with time because of abrasion of the teeth of the driving gear and driven gear due to steering, it is possible to satisfactorily eliminate backlash and to prevent noise from being generated by backlash and heard inside the compartment of an automobile.
According to the third invention, in the first invention, it is possible to eliminate backlash without changing the supporting point of the driving gear.
According to the fifth invention, in the third invention, even when the driving gear is hypoid pinion integrally coupled to one end portion of the rotating shaft of the motor as the supporting shaft, it is possible to swing the driving gear in a simple manner.
According to the sixth invention, in the fifth invention, the rotating shaft rotates a slightly clockwise centering with the first bearing because the second bearing is energized downwardly. Accordingly, the driving gear provided on the left end portion of the rotating shaft is energized upwardly and can securely mesh with the driven gear.
According to the eighth invention, in the third invention, since the center of rotation of the driving gear and that of the rotating shaft can be arranged to cross each other, even when the deflection of the driving gear increases, it is possible to eliminate backlash while retaining the rotating characteristic of the driving gear.
According to the tenth invention, in the eighth invention, since the driving gear is energized via the fourth bearing, it is possible to satisfactorily retain the rotating characteristic of the driving gear and satisfactorily prevent positional displacement of the meshing point of the driving gear and driven gear.
According to the second, fourth, seventh and ninth inventions, in the first, third, fifth and seventh inventions, it is possible to apply the elastic restoring forces of the protrusions to the driving gear via the bearing and energize the driving gear toward the driven gear. Therefore, even when the meshing state of the driving gear and driven gear changes with time because of dimensional errors of parts such as the driving gear and abrasion of the teeth of the driving gear and driven due to steering, it is possible to automatically eliminate the clearance between the driving gear and driven gear and to satisfactorily eliminate backlash. In addition, when number of the protrusion is one or two, accurate assembling becomes hard, so that it is becomes hard to prevent the positional displacement of the meshing point of the driving gear and driven gear.
Moreover, since at least three protrusions come into contact with the bearing and energize the bearing from at least three positions along a circumferential direction, it is possible to satisfactorily prevent positional displacement of the meshing point of the driving gear and driven gear. Furthermore, even when a rotational torque applied to the meshing point of the driving gear and driven gear generates a force for separating the driving gear from the driven gear, the movement of the bearing with respect to the elastic member can be limited by the intermediate protrusions, thereby preventing the bearing from coming into contact with the elastic member and generating noise.
According to the eleventh invention, in the first invention, even when the ambient temperature of the driven gear increases and the clearance between the housing and the bearing in the axial direction increases because of the difference in the coefficient of thermal expansion between the housing made of aluminum and the bearing made of iron, the movement of the bearing and driven gear in the axial direction due to this clearance can be satisfactorily limited by the elastic member, thereby automatically eliminating the clearance between the driving gear and driven gear and satisfactorily eliminating backlash.
The above and further objects and features of the invention will more fully be apparent from the following detailed description with accompanying drawings.